OBJECTIVE: To describe a woman with a nonmosaic (45,X) form of Turner's syndrome who gave birth to a girl with 45,X Turner syndrome. DESIGN: Patient report. SETTING: Outpatient clinic of a university hospital. PATIENT(S): A woman with typical phenotypic features of Turner syndrome and a 45,X karyotype and her daughter with the same karyotype. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Routine karyotype analysis on 200 white blood cells on two different occasions, on skin fibroblasts (1,000 mitoses) and on ovarian fibroblasts. Translocation of X-chromosome material was investigated by a complete X paint and fluorescent in situ hybridization analysis. RESULT(S): The patient had a spontaneous puberty and became pregnant on three occasions. Her first daughter has a normal karyotype, the second pregnancy ended in spontaneous abortion, and after the third pregnancy, a girl was born with a 45,X karyotype. Karyotype analysis of a large number of mitoses in three different cell types failed to demonstrate any mosaicism. Translocation of X-chromosome material was ruled out by fluorescent in situ hybridization analysis with an X paint. CONCLUSION(S): This is a rare case of pregnancy in a nonmosaic Turner syndrome patient and, to our knowledge, is the only one that resulted in a live-born baby with the same karyotype. Cryptic mosaicism could not be found despite thorough investigations. Some hypotheses are presented that may explain this unique event.